1. Field of the Invention
The present invention relates to a process of producing an assembled camshaft or the like consisting of a shaft tube and slid-on elements by expanding the shaft tube in the region of the elements by applying internal pressure; it further relates to an assembled camshaft or the like consisting of a shaft tube and slid-on elements produced by expanding the shaft tube in the region of the elements as a product. The above-mentioned slid-on elements may be control cams, bearing rings and gear wheels or bevel gears which have to be connected to the shaft tube in a non-rotating and true-to-angle way.
2. Description of the Prior Art
There are prior art camshafts in which finish-machined cams and bearing rings are shrunk on to a shaft tube, following thermal processes (DE-OS 33 01 749). With such shafts the selection of the material for the elements is limited in that certain specific heat expansion coefficients of the materials are required for the shrinking process to be able to produce the necessary fits. In order to ensure sufficient tension between the shaft tube and the elements to achieve a non-rotating connection, the shaft material, too, has to meet certain more stringent requirements in respect of strength and surface hardness. Because of the necessary thermal treatments, joining the shaft tube and the elements is time-consuming and complicated. The increase in temperature in the course of the joining operation inevitably leads to a hardness loss of the elements.
There are other prior art camshafts in the case of which individual cams are slid on to profiled bars in a form-fitting way and connected to these by, for instance, shrinking, freezing, soldering, welding or glueing (DE-OS 23 36 241, DE-GM 79 20 957). This process does not permit any weight advantages as compared to conventional camshafts; modifying or adapting the angular position of the cams requires a complete redesign of the components.
It is also known to connect a camshaft consisting of a hollow shaft and longitudinally and circumferentially grooved bearing seats and cams by expanding the shaft tube section by section by applying internal pressure and pressing it into the grooves (DE-PS 25 46 802). In this case, the cams having a uniform wall thickness are tube-like so that a continuous fit on the shaft is impossible, which means that the strength of the cams does not appear to be ensured.
Finally it is known to fix internally round cams and bearing seats on a shaft tube purely by force-locking means by expanding the shaft tube along its entire length by applying internal pressure, and in order to maintain the pressure fit the tube, because of its thin walls, has to be filled with a synthetic substance (DE-PS 32 27 693). Without this additional measure it has so far not been possible to produce a secure fit capable of being torque-loaded. When expanding the shaft along its entire length there is an inherent risk of bulging in the regions between the cams, and there may be a notch effect at the end faces of the cams which reduces the strength of the shaft.